In the field of vehicle body structure, it is known to connect a rear end of each front side frame to front ends of a front inside sill and a center frame via an outrigger or the like (See JP 2009-18725A, for instance), and to use a floor frame extending in the fore and aft direction between each front inside sill and a center frame (floor tunnel frame) and having a front end connected to the rear end of a front side frame and a rear end connected to a middle cross member located under the rear seat (See JP 2009-6902A and JP 2009-6903A, for instance).
The floor frames allow the frontal crash load applied to the front side frames to be transmitted to the rear part of the vehicle body via the floor frames in addition to the front inside sills and center frame. By thus increasing the possible paths of the frontal crash load, the transmission of the frontal crash load to the rear part of the vehicle body is performed in a highly efficient manner, and this improves the crash performance of the vehicle body. Furthermore, by welding the floor frames to the floor panel, the stiffness of the floor panel is increased, and this contributes to the NV (noise and vibration) performance of the vehicle body.
However, according to the prior proposal, as the floor frames extend over the entire fore and aft extent of the floor panel, the weight of the vehicle body may undesirably increase. Furthermore, the increased number of welding spots increases the manufacturing cost and reduces the manufacturing efficiency.
Also, in an automotive floor structure, it has been proposed to stamp form dimples defined by a three-dimensionally curved surface in the floor panel with the aim of increasing the stiffness of the floor panel and improving the NV performance of the vehicle body. See (See JP 2004-237871A, for instance).
However, the dimples prevent the floor panel to provide a flat floor surface. In particular, if the dimples extend over large areas and define gradual curves, the carpet placed on the floor surface follows the contour of the dimpled floor surface, and this impairs the comfort of the vehicle occupant. If the floor surface includes slanted areas, the vehicle occupant may be unable to stand of the floor in a stable manner. If the vehicle occupant moves about on the floor, his or her foot may stumble upon floor irregularities, and may experience some discomfort.
Conventionally, such problems were overcome by placing a thick under pad typically made of thick urethane mat or a stiff board under the carpet. But this requires an additional component, and impairs the production efficiency, manufacturing cost and resources saving efforts.